This application claims the benefit of French Application FR 06 01889, filed Mar. 3, 2006.
In patients fitted with an artificial joint, such as for example a hip prosthesis, it is not rare for it to be necessary to proceed with replacement of the implanted member, either because of mechanical deterioration or because of infectious complications affecting the implant area and giving rise to detachment of the prosthesis. It is then necessary to withdraw the prosthesis and provide antiseptic and antibiotic treatment before replacing a permanent implant. All this operation, known as “two-stage prosthesis replacement” lasts for several weeks, or even several months, because it is essential that the infection should be completely treated by broad spectrum antibiotic treatment associated with local antibiotic treatment before any implant is refitted.
In order to prevent tissues (muscles, tendons, bone) from occupying the space released by removal of the permanent prosthesis, a spacer which temporarily replaces the prosthesis in the joint area is fitted. Thus the risk of the formation of a haematoma and superinfection is reduced, and the limb is better stabilised. Furthermore the patient retains some mobility during the transitional period and ultimately fitting of the permanent prosthesis is made easier.
Spacers are commonly made of relatively cheap materials such as polymer cements, very often polymethyl methacrylate (abbreviated to PPMA). Use of such a polymer has the advantage that it makes it possible for the implant area to be maintained and the infection to be treated locally. In fact because of its cross-linked structure it can be combined with an antibiotic agent which diffuses into the surrounding tissues and thus provides prolonged local treatment for the infection. The antibiotic is progressively released by diffusion in body fluids which are then transported to adjacent tissues.
The antibiotic systematically used in bone surgery is gentamycin, which is a broad spectrum antibiotic. However, given the increase in the level of resistance of bacteria isolated in cases of infection of the hip in particular, recent studies have envisaged the use of a combination of antibiotics in PMMA spacers, such as for example gentamycin and vancomycin (Bertazzoni Minelli E. et al., Journal of Antimicrobial Chemotherapy 2004, 53, pp. 329-334). For this purpose premoulded spaces loaded with commercial gentamycin have been pierced with holes and filled with a cement loaded with vancomycin, this technique making it possible to avoid interference in release of the two antibiotics by the PPMA and adjust the rate of elution for each antibiotic. These tests have demonstrated the effectiveness of combined use of two antibiotics in the local treatment of infections in joint prostheses during two-stage replacements, also with regard to strains which are resistant to conventional treatments. However introduction of the second antibiotic into a spacer which has been preloaded with gentamycin requires difficult manipulation which is hard to reproduce, and which is contrary to safety and quality of care.